I have been doing E-6 for almost 25 years with nothing more sophisticated than a sink full of water (at the right temp) and ordinary B&W developing drums/tanks. I used to use a Beseler E-6 developer. When it became extinct, I switched to "Agfa Process 44".

I find that the extremely tight temp requirements are more "C.Y.A." frorm the manufacturer. I have had temperature deteriorate 5 degrees F between the start of the process and the last bath with no detectable difference on the slides. (Manitoba winters are COLD; sometimes keeping something at 100F would require military flame throwers!)

I am now working in 4x5 using a Combi-Plan tank which requires 1.0L of solution so I work with a double batch of (500mL) Agfa chems. A double batch costs about $36 (Canadian). I usually save up my transparency films until I have enough to justfy mixing chemicals and I have yet to exhaust a set of chemistry. Agfa claim .45 square Meters per batch but I have run beyond that with no problem. I have also pushed the shelf life to nearly double with good results.

I am sure, if you were running a professional lab, staying within the manufacturer's recommendations is wise. If you are a hobbiest and the pictures are non-critical, so is the process ;-)